Engineering

Engineering sits at the intersection of big data, AI, and massive scale - solving deep complexity behind the scenes. Behind the scenes are powerful systems that feel remarkably simple to every customer

Email Analyzer Apollo Blog

January 28, 2026

The Email Analyzer That Explains Itself

Apollo's Email Analyzer helps SDRs write better cold emails with instant, actionable feedback - built by using ML to discover rules, not just make predictions.

AI

Engineering

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Developer Productivity

Engineering Leadership

How We Measured AI Tooling Productivity Gain Across 250+ Engineers at Apollo.io

At Apollo.io, we ran a company-wide experiment across 250+ engineers to quantify the real productivity impact of AI-powered developer tooling. This post breaks down the metrics we chose, the methodology behind the experiment, and the hard lessons we learned about measuring engineering productivity without gaming the system.

January 16, 2026

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A Reliable Testing and Evaluation Suite for AI Assistant

At Apollo, we engineered a custom AI Assistant Regression Suite to reliably test a multi-agent, multi‑turn AI assistant by converting real production conversations into replayable tests that semantically match intent while verifying side effects.

December 2, 2025

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A modern, spreadsheet UI for Enriching CRM data

ApolloHacks 2025 sparked one of Apollo’s an exciting design innovation: the Spreadsheet UI to enrich CRM data. Designed for speed, simplicity, and scale, it transforms complex enrichment workflows into an intuitive, spreadsheet-like experience. Users can view, update, and enrich thousands of records with minimal clicks and real-time feedback, all within a single, unified grid. Backed by powerful virtualization and smart interaction design, this modern UI delivers high performance and clarity for data-driven teams.

October 27, 2025

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Intelligent Email Deliverability Debugging

Apollo transformed email deliverability with an AI-powered agent that cuts debugging time from weeks to minutes. Built with the ReACT framework, it systematically analyzes metrics, authentication, bounce logs, and domain setup to pinpoint issues and offer real-time solutions. Continuous evals ensure reliability, while an updated knowledge base keeps the agent current with Apollo’s evolving features. By combining systematic analysis with domain expertise, Apollo turned a complex, frustrating process into a streamlined, AI-assisted experience, helping users maximize inbox reach and ROI faster than ever before.

September 17, 2025

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AI Tagging : From Feedback To Actions

Apollo automated customer feedback tagging with AI + LLMs, scaling VOC insights, boosting CIR accuracy, and reducing manual effort—transforming customer complaints into product action.

August 26, 2025

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Pierogis & Pull Requests: Apollo’s Poland Offsite

There’s something magical about seeing your remote teammates materialize in real life. You know these people through GitHub comments, Zoom calls, and Slack messages. But suddenly, they’re there in a Kraków 🇵🇱 hotel lobby, holding a coffee, making actual eye contact. And for a moment, your brain short-circuits. From July ...

August 19, 2025

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Friction to Fortress: How Turnstile Shields Apollo

Apollo engineered a modern, privacy‑first security system using Cloudflare® Turnstile to block millions of malicious login and API attacks without disrupting legitimate users. By combining adaptive challenges, edge enforcement, and data‑driven signals, we reduced operational overhead, improved login success rates, and protected user trust at scale — all while preparing for future growth.

July 29, 2025

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Waterfall: A Modular, Rate-Aware Data Engine

"Discover how Apollo’s Data Waterfall engine transformed multi-vendor data enrichment—delivering higher fill rates for emails and phone numbers, faster scaling, and lower costs for millions of enriched contacts daily.

July 25, 2025

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ApolloHacks '25 : Part I

Unlocking new growth, Apollo’s latest edition of their annual hackathon ApolloHacks 2025 delivered two game-changing projects: a multi-lingual website to reach non-English speaking markets, and a mobile-first experience that empowers sales teams to access data and update leads from anywhere. With these innovations, Apollo IO is now more global and truly on the go.

June 4, 2025

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Speedy Search Via 2-Phase Scoring

How We Tamed Complex Queries Without Slowing Down the Universe If you’ve ever built a search engine that supports custom scoring , you’re probably familiar with the “Latency Monster” that shows up as your scoring logic grows more complex. At Apollo, our users define intricate scoring criteria—“Give me +30 points ...

May 27, 2025

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Fighting Noise In Email Tracking

Email engagement signals like opens and clicks help sales teams trigger workflows and prioritise leads. But providers like Google and Apple now use bots to scan emails, inflating open rates and distorting real engagement. Apollo solves this by filtering out bot activity, helping teams focus only on genuine human interactions and drive better conversions.

April 24, 2025

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Prospect Recommendation 2.0

Discover how Apollo enhances prospect recommendations with team collaboration and index optimization, boosting coverage, reducing costs, and maintaining accuracy. Join us in our AI-driven journey!

April 14, 2025

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Cross-Entity Searching

Cross-Entity Searching - Part 1

At Apollo, our mission to build a leading Sales Platform brings with it a variety of complex customer use cases. Our goal is to support these use cases in the most intuitive and user-friendly manner possible. One such intricate challenge is enabling searches across multiple Apollo entities ...

April 2, 2025

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Apollo IO

A fresh look at Apollo: elevating our visual identity

Apollo’s design refresh unifies brand and product, enhancing clarity, usability, and aesthetics with a new identity, dark mode, and a scalable design system. Learn how Apollo’s design and engineering team pulled it off!

February 21, 2025

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Detecting Data Duplication at Scale

Discover how Apollo.io tackled duplicate accounts with a scalable deduplication tool. Learn about root cause analysis, data pipelines, and automation that improved data quality, reduced customer escalations, and enhanced operational efficiency.

January 29, 2025

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Distinguished Engineer Series: Aidan Li, Sr Director - Product, Platform & Growth

Today, we talk about Aidan Li, Apollo’s Director of Engineering for Core Product, Platform, and Growth, who embodies technical excellence and leadership. Starting as a Software Engineer in 2019, Aidan has been a driving force behind Apollo’s growth—building company-wide frameworks, improving incident management, and leading key product initiatives. His people-first approach, mentorship, and problem-solving make Apollo a place where engineers thrive and innovate. If you’re looking for a place to grow with exceptional leaders, Apollo is the perfect fit.

January 10, 2025

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Building Apollo's New Home

Discover how Apollo's new personalized homepage, powered by a Dynamic Page Framework and modular Widgets Library, enhances feature discovery, user productivity, and ROI through customization at scale.

December 17, 2024

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Getting Launch Ready : Quality & Resilience On Production

Writing production-ready code is crucial for building robust, fault-tolerant systems. This guide highlights common pitfalls and provides actionable steps to improve code quality, ensuring reliability and minimizing failures. Let’s dive in⚡️.

November 8, 2024

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Email Reply Classification Done Right

At Apollo.io , we're constantly working to improve our platform for Sales Development Representatives (SDRs) across various organizations. One common challenge our users face is managing the overwhelming volume of email responses they receive daily. SDRs often struggle to quickly identify and prioritize important replies amidst a sea of out-of-office ...

August 23, 2024

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Solving ID type confusion in Mongoid

Apollo’s Context Apollo.io backend codebase is fully based on Ruby on Rails and contained within a single GitHub Monorepo. This allows us to centralize quality control, and database communication. We also use multiple MongoDB clusters with collections containing billions of documents. It’s crucial for developer productivity to have a common ...

August 9, 2024

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The mentor I never knew I needed 🪄

🌴 Branching my way out of the deep end There was a project which was essentially a “relay race” of engineers working in sequence. Before we started, I had a chat with Umang, my mentor and Staff Frontend Engineer for the Growth team, about how to handle merging my changes ...

August 9, 2024

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Detecting Dangerous MongoDB Queries

📈 Querying MongoDB at scale Here at Apollo, we use MongoDB as our main database store and Mongoid on Ruby as our interface to the DB. The larger collections that are routinely used by our user-facing features can range from tens of millions to tens of billions of documents, so ...

July 10, 2024

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Orum Apollo

Building the Orum Integration with Apollo

I’m Melissa Reffsin, Product Manager at Orum. You might be wondering who I am, what Orum is, and what I’m doing writing an article for Apollo’s new tech blog! What Is Orum ? Orum is an AI-powered live conversation platform driving more pipelines for sales organizations. With Orum, users automate ...

April 10, 2024

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analytics at apollo

Analytics at Scale @ Apollo.io

Apollo seeks to empower GTM teams with an end-to-end platform for all their sales needs, from finding the right customers to winning deals. Within every step in their journey at Apollo, analytics enables customers to deep dive into their metrics and performance. Like a trusted “sherpa”, ...

April 10, 2024

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photo of Himanshu Gahlot

Distinguished Engineer Series: Himanshu Gahlot, VP Engineering, Data and Intelligence

Himanshu Gahlot, a Senior Director of Engineering at Apollo.io, brings a wealth of experience and expertise to the tech domain. Currently overseeing data and machine learning initiatives, he leads a globally distributed team of 100+ individuals across various verticals. Most importantly, he’s also my boss, so I wanted to highlight ...

January 31, 2024

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Abstract Image of a System

Building Apollo’s Data & Machine Learning Platform

Data is at the core of Apollo’s business. The company started as a sales prospecting data vendor before becoming the all-in-one sales platform. Sales prospecting continues to be the one of the most fundamental and important parts of our business portfolio. Building and maintaining such a big data business comes ...

January 24, 2024

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Engineering Focus and Rest Days

In the fast-paced world of technology, fostering an environment that nurtures innovation and productivity is paramount. At Apollo, we understand the importance of providing our engineering teams with the ideal conditions to excel in their work. I wanted to throw together a blog post to talk about a few angles ...

January 24, 2024

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